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Water absorption is a key property in several tissue paper materials and can be a differentiating factor in terms of consumer choice. The converting modifications applied in the tissue industry can improved absorbency properties. For this purpose, the main goal of the present work is to study the influence of “deco” and “micro” embossing on water absorption capacity, Klemm capillary rise, and liquid spreading kinetics in tissue papers. An industrial never-dried bleached eucalyptus kraft pulp, a creped industrial base tissue paper, and a disintegrated fibrous suspension obtained from the same industrial paper were used to produce structures with and without “deco” and “micro” embossing patterns. The results indicate that the “micro” embossing process promoted bulky and porous structures, enhancing water absorption capacity and Klemm capillary rise properties, while the “dec” embossing pattern decreased water absorption capacity properties. The creping process also increased the water absorption capacity but decreased Klemm capillary rise properties along with the fiber mixtures. Regarding the liquid spreading kinetics, both embossing patterns decreased this property in uncreped isotropic structures, contrary to creped anisotropic structures. The eucalyptus and softwood fibers mixture improved the spreading kinetics compared to the creping process. The performance of structures with and without embossing allowed to quantify the liquid retention properties, combining ISO experimental methods and an optical system that records the liquid interaction with fibrous structures. In conclusion, this laboratory embossing method can be used as an alternative method to optimize converting operations and the final tissue paper characterization, on a laboratory scale.

This study introduces an innovative approach for developing high strength-high softness recycled fibers through soft mechanical treatment. Recycled fibers from old corrugated containers were treated using a homogenizer, a refiner, and in tandem. The recycled fibers and tissue paper sheets after the treatments were evaluated for the effect on critical properties such as fiber morphologies, freeness, water retention, hard-to-remove water, bulk, softness, tensile strength, and water absorption. High softness and tensile strength were achieved with mechanical treatment by utilizing a homogenizer alone or in tandem with a refiner. Overall, the homogenized recycled fibers and tissue paper sheets provided higher bulk, water absorption, and tensile strength while maintaining the softness and drainage (freeness) behavior similar to unrefined paper sheets. It was found that homogenization helps in deflocculating the recycled fibers without negatively affecting the fiber quality, such as fines generation.

Abstract The surface of tissue paper is relatively complex compared to other paper grades and consists of several overlapping structures like protruding fibres, crepe and fabric-based patterns at different spatial frequencies. The knowledge of tissue surface characteristics is crucial when it comes to improvement with respect to surface softness and the perceptual handfeel of tissue products. In this work we used the optical based, non-contact measurement principle of focus variation for surface characterization of dry-creped, textured and through air dried (TAD) tissue. Based on the three tissue grades, a procedure which includes the characterization of the whole tissue surface throughout different scales within one setup, was developed. Surprisingly, focus variation was rarely used in tissue-related research, as it provides robust and reliable 3D surface information which can be used for further areal surface analysis. Special attention was given to the preparation and discussion of the raw data up to the final analysis including several spatial filtering steps. Enhanced surface parameters like the developed interfacial area ratio (Sdr) and the power spectral density (PSD) were used to describe the surface adequately. The surface roughness of the three tissue grades was compared, with the textured tissue showing the highest roughness in Sdr and PSD analysis. Although both methods are based on different principles, a high correlation in terms of evaluated roughness is evident. Regular structures like crepe and patterns are obtainable as peaks at the respective frequency with a certain intensity in the PSD evaluation. Apart from topography in terms of structures and roughness, the wide field of view of the focus variation measurement also allows assessment of effects related to flocculation and sheet formation. The developed procedure could also be appropriate for other fibre based materials and/or fabrics, which are similar to tissue with respect to optical properties such as for example nonwovens. Graphic abstract

Abstract Tissue paper softness relies on two major factors, the bulk softness, which can be indicated by the elasticity of the sheet, and surface softness. Measurement of surface softness is complicated and often requires a multi-step process. A key parameter defining surface softness is the topography of the surface, particularly the crepe structure and its periodicity. Herein, we present a novel approach to measure and quantify the tissue paper surface crepe structure and periodicity based on the detection of waviness along the sample using laser scanning confocal microscopy (LSM) and X-ray tomography (XRT). In addition, field emission scanning electron microscope (FESEM) was used to characterize the tissue paper surface. We demonstrate that surface topography is directly correlated to the erosion of the doctor blade, which is used to remove the dry tissue paper from the Yankee cylinder. Because of its accuracy and simplicity, the laser confocal microscopy method has the potential to be used directly on the production line to monitor the production process of the tissue paper. XRT revealed more structural details of the tissue paper structure in 3D, and it allowed for the reconstruction of the surface and the internal structure of the tissue paper. Graphic abstract

A comparison between uncreped and creped handsheets was performed to study the effect of fiber morphology and creping process on fiber web structure and tissue properties. Four wood and non-wood pulps refined at different levels were used to manufacture uncreped and creped handsheets using a creping simulator. A characterization of the fiber web structure using scanning electron microscopy (SEM) and evaluation of tissue properties (e.g. tensile strength, water absorbency, softness) was performed on the uncreped and creped handsheets. The results obtained with the creping simulator were compared with commercial products to evaluate the significance of the creping simulator results. The SEM images of the fiber web structure showed that the creping process promoted buckling and distortion of fibers, delamination of surface fiber layer, development of free fiber ends and creation of crepe folds, which enhanced water absorbency and softness at the expense of reduced tensile strength. Short and thin fibers seemed to be more effectively creped than long and coarse fibers. Long and coarse fibers seemed to offer higher resistance to the compressive forces acting at the creping blade. A reasonable correlation between the performance of uncreped and creped handsheets made with different fibers was observed. The results indicate that the performance of uncreped handsheets can be used as a semi-quantitative indication of the performance of creped handsheets. The performance of the creped handsheets were similar to commercial products, which indicates that the creping simulator can be used as an alternative to study the creping process at laboratory scale.

Tissue paper that is prepared from bamboo has a very promising future in the world, especially in China, thanks to the various merits of bamboo fibers. However, the water absorption behavior and mechanical properties of bamboo pulp based tissue paper need to be improved due to the inherent drawbacks of bamboo fiber, such as high stiffness, weak interaction between bamboo fibers etc. Hence, cellulose nanofibers (CNFs) were combined with bamboo fibers before the tissue paper-making process, to improve the water absorption behavior and mechanical properties of tissue paper. The hypotheses are that: (1) CNFs themselves possess large specific surface area and abundant hydroxyl groups as well, thus enhancing the hydrophilicity of tissue paper; and (2) the added CNFs can form 3D structures in tissue paper, thus providing abundant pores with uniform small size, which would facilitate the capillary effect for water absorption; and (3) more hydrogen bonds will be formed between CNF and bamboo fibers, thus improving the strength properties of tissue paper, thanks to the excellent mechanical and physical properties of CNF. The results from water absorption and tensile strength tests of bamboo handsheets indicated that the addition of CNFs can increase the water absorption capacity from 6.6 to 8.7 g/g when the CNF dosage was 10 wt% (based on the dried pulp). The water retention value of prepared bamboo fibers increased from 163 to 190% at the same CNF dosage, the tensile index increased from 18.5 to 24.5 N m/g as well. The results from the bulk and pore size analyses, FTIR, as well as SEM images of tissue paper also evidenced the conclusions above. Cellulose nanofiber (CNF) as a versatile filler for the preparation of bamboo pulp based tissue paper with improved water absorption behavior and mechanical properties

Tissue furnish optimization plays a key role in enhancing tissue properties, making the process cost-effective. Typically, this furnish is composed of a mixture of hardwood eucalyptus fibers (HW) and softwood (SW) fibers, which ensure strength and tissue machine runnability. However, the tissue paper production with the maximization of eucalyptus fibers achieves softer papers at less cost, since SW fibers are often more expensive than HW fibers. From this perspective, this study aims to investigate the effect of micro/nano-fibrillated cellulose (MFC/NFC) as an additive, on structural, softness, strength, and water absorption properties of tissue papers, promoting partial or total removal of SW fibers to produce 100% eucalyptus materials. MFC/NFC was characterized in terms of morphological, chemical, and water interaction properties. The results showed that MFC/NFC presents a high bonding surface area, high carboxyl group content and, when incorporated into tissue furnishes, it promotes strong inter-fiber bonds. This evidence was also supported by SEM image analysis methods and FTIR. Additionally, laboratory tissue handsheets with low basis weight were produced and used in the characterization assays. Overall, the results indicated that MFC/NFC improved strength, at the expense of bulk, porosity, softness, and absorption properties. Compared to typical industrial furnish mixtures (75%HW + 25%SW), MFC/NFC enhanced the production of bulkier, porous, and softer structures, but with reduced strength and absorption. It was possible to optimize the furnish composition by using fiber modeling to obtain 3D structure computation simulations with predictive capability. The MFC/NFC proved to be a high-quality additive to improve softness and strength properties.

Composites of cellulose fibers were made with paper-making technology. Two types of microfibrillated cellulose (MFC), obtained by with either homogenization or ball milling, were blended with hardwood fibers to give composites having high strength and low air permeability. The strengthening effects of the MFCs were compared with strengthening by cellulose microparticles (CMPs) made by cryogenic milling, with and without polyamideamine-epichlorohydrin addition. The MFC from homogenization was fully retained on the fiber web due to a broad size distribution; in contrast, the retention ratio for MFC produced by ball milling was lower than 50 % because of its smaller particle size. The small size caused the resulting paper to display a more compact and denser structure. The main distinction between the papers made with the two types of MFC was the elongation at break under wet conditions, suggesting that they reinforce the paper in different ways. On the other hand, CMPs act as mechanical debonders and could find application in tissue paper, increasing paper bulk and decreasing the density and thus improve tissue softness.

Currently, bleached eucalypt pulps are largely used for printing and writing (P&W) and sanitary (tissue) paper grades. Among the many pulp quality requirements for P&W and tissue paper production the xylan content is one of the most significant. For P&W papers, increasing xylans improve pulp refinability and strength properties but negatively affect bulk and drainability. For tissue paper, xylans are purportedly advantageous during paper drying in the Yankee cylinder but negatively affect paper bulk and may increase dusting during paper manufacture. On the other hand, bleachability is a very important parameter for both P&W and tissue grade pulps since bleaching cost is the second most significant in eucalypt bleached kraft pulp production. The aim of this study was evaluating the influence of eucalyptus pulp xylan content on its bleachability, refinability and drainability. A sample of industrial unbleached eucalyptus kraft pulp containing 15.6 % xylans was treated with various alkali charges at room temperature in order to obtain materials with different xylan contents. The pulps were bleached to 90 % ISO brightness with the O–DHT–(EP)–D sequence and evaluated for their refinability and drainability. By increasing the alkali concentration in the range of 10–70 g/L pulps of 14.5–5.9 % xylans were produced with no significant impact on cellulose crystallinity. The decrease of xylan content significantly decreased pulp bleaching chemical demand, water retention value and refinability and increased pulp drainability.